Isolated frame on platforms stabilized by spinning body

ABSTRACT

A despun platform is stabilized by a spinning body. A frame is mounted on an isolation pivot on the despun platform. A directable instrument is mounted on the frame to isolate the instrument from platform perturbations. The isolation pivot substantially isolates the frame from wobble caused by rotation of the spinning body about an axis other than the bearing axis of the despun platform. An optional damping mechanism at the isolation mount activated by relative motion between frame and despun platform damps frame motion with respect to the despun platform. For the case where frame moment of inertia is sufficiently high, nutation damping is provided by this mechanism.

United States Patent [1 1 Reiter et al.

[ ISOLATED FRAME ON PLATFORMS STABILIZED BY SPINNING BODY [76]Inventors: Gordon S. Reiter, 13900 Panay Way, Apt. S'32l, Marina delRey, Calif. 90291; Charles P. Rubin, 3139 Coolidge Ave., Los Angeles,Calif. 90066; Ronald V. Swanson, 2023 Redondela Dr., San Pedro, Calif.90732; Bernard F. Burns, Jr., 906 11th St., Manhattan Beach, Calif.90266; Anthony J. Iorillo, 551 Paseo Miramar, Pacific Palisades, Calif.

[22] Filed: May 11, 1973 [21] Appl. No.1 359,290

Related U.S. Application Data [63] Continuation of Ser. No. 151,327,June 9, I971,

OTHER PUBLICATIONS Hughes Gyrostat System, Public Relations Dept.,

[ 51 Apr. 15, 1975 Aerospace Group, Hughes Aircraft Company, October,1967.

Hughes System Make Giant Improved Satellites Possible, Hughesnews,Hughes Aircraft Company, Vol. 26, No. 22, pp. 1, 4.

Laboratory Dynamic Model, Public Relations Dept., Aerospace Group,Hughes Aircraft Co., No. 8500273.

Primary Examiner-Trygve M. Blix Assistant ExaminerBarry L. KelmachterAttorney, Agent, or Firm-Allen A. Dicke, Jr.; W. H. MacAllister [57]ABSTRACT A despun platform is stabilized by a spinning body. A frame ismounted on an isolation pivot on the despun platform. A directableinstrument is mounted on the frame to isolate the instrument fromplatform perturbations. The isolation pivot substantially isolates theframe from wobble caused by rotation of the spinning body about an axisother than the bearing axis of the despun platform. An optional dampingmechanism at the isolation mount activated by relative motion betweenframe and despun platform damps frame motion with respect to the despunplatform. For the case where frame moment of inertia is sufficientlyhigh, nutation damping is provided by this mechanism.

2 Claims, 10 Drawing Figures PATENTEEAFR '5 V SHEET 10F 4 Fig. 9.

r n 6 n e R S n 0 d r O G Charles P. Rubin,

Ronald V. Swanson,

Bernard F. Burns, Jr. Anrhony J.Iori|lo INVENTORS ALLEN A. DICKE, J R.

Fig.2.

AGENT.

PATENTEBAPR 1 5197s Fig.5

I: :1 n4 -"G 7s SHEET 3 OF 4 Fig.6.

FATEFHEBAFR I 5 SHEET 1, 0F 4 F i g. 10. (PRIOR ART) ISOLATED FRAME ONPLATFORMS STABILIZED BY SPINNING BODY CROSS REFERENCE This applicationis a continuation of patent application Ser. No. 151,327, now abandonedfiled June 9, 1971 by Gordon S. Reiter, Charles P. Rubin, Ronald V.Swanson, Bernard F. Burns, .Ir., and Anthony J. lorillo for DirectableInstrument Carrying Isolated Frame.

BACKGROUND This invention is directed to a frame carrying a directableinstrument which is mounted on a platform through the agency of motionisolation devices, with the platform being stabilized by a spinningbody, such as a gyroscopic mass.

The stabilization of devices upon which instruments are mounted, whetheron the ground or in space, can be accomplished in several differentways. One of these means for stabilizing a platform comprises thespinning of a flywheel mass. The ordinary flywheel is a rigid structurewhich rotates about the axis of maximum moment of inertia of the system.This is the only stable rotative condition for an undamped system. Aplatform is rotatably mounted upon a rotational axis corresponding asclosely as possible to the spin axis so the platform has minimum wobbledue to minimum deviation between these two axes. Such a platform isnormally sufficiently stabilized for use as an instrument or equipmentplatform. However, isolation from bearing inaccuracies or the slightwobble which is likely to be present can be accomplished by theinvention described below.

In another case of similar equipment, the spinning body is a gyroscopicmass which also rotates about the axis of maximum moment of inertia.However, in order to employ useful equipment as part of the gyroscopicmass, instruments and equipment are mounted thereon. However, suchinstruments or equipment may change in mass or mass distribution. Thisis particularly true, if liquid fuel tanks or other liquid-containingdevices are mounted on the gyroscopic mass, due to fuel usage and liquidsloshing. Of course, the spinning gyroscopic body continues to rotateabout the axis of maximum moment of inertia. However, this axis maychange slightly from time to time, with the result that the spin axismay move away from the axis of the bearings through which the despunplatform is mounted upon the spinning gyroscopic body. This causeswobble of the despun platform. The wobble is a direct function of spinspeed and a direct function of rotation of the spinning gyroscopic massabout a spin axis which is other than the bearing axis. The wobble maybe conical or it may be purely translational, or a combination of both,depending on whether or not the changes in the mass of the spinninggyroscopic body are in the plane of the center of gravity normal to thespin axis. Such a stabilized device does not need damping to maintainits stability.

Another type of device is described in A. J. lorillo U.S. Pat. No.3,442,468, granted May 6, 1969, and directed to a Nutation DampedStabilized Device. This patent describes a stabilized despun platformfor a situation where the spinning body is rotating about an axis otherthan the axis of maximum moment of inertia of the system. The ratio ofthe total transverse moment to the spin inertia is greater than one.Thus, the lorillo patent teaching permits design flexibility to design aspinning gyroscopic mass which can be longer and not have such a largediameter, in the sense of the axis of rotation. The entire disclosure ofthat patent is incorporated herein by this reference. The patent teachesthat, when a nutation damper is applied to the despun platform, thesystem can be made stable, even though the spinning body is not rotatingabout the axis of maximum moment of inertia. Nutation occurs in suchcircumstances, and nutation frequency is related to the mass and momentsof inertia about the various axes, as well as the spin speed. Thenutation frequency is normally less than the wobble frequency. Thenutation damper of the lorillo patent is preferably designed for thatparticular nutation frequency.

SUMMARY In order to aid in the understanding of this invention, it canbe stated in essentially summary form that it is directed to a frame forcarrying a directable instrument thereon mounted upon a platform bymeans of isolation mountings, which platform is rotatably connected to aspinning body which stabilizes the platform.

Accordingly, it is an object of this invention to separate a platformfrom its stabilizing spinning rotor by means of a flexible joint, andseparate a frame from the platform by an appropriately soft spring jointto reduce the response of the frame caused by the forced motion of rotorimbalances. It is a further object to provide an isolated frame for themounting of optical devices, directional equipment, or radio frequencyequipment, which frame is isolated from a platform, and which platformis stabilized by a rotating body, the entire structure being capable ofbeing employed as a space vehicle or as an earth-based, stabilized framefor such optical or radio frequency equipment. It is still a furtherobject to improve, by a sizable factor such as 10, the directionalstability of a frame, as compared to the stabilized platform upon whichit is mounted.

Other objects and advantages of this invention will become apparent froma study of the following portion of the specification, the claims, andthe attached drawlngs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of avehicle, in this case, a mock-up of the spacecraft for the testing ofinstrumentation, having the frame mounted by isolation supports on theplatform, in accordance with this invention.

FIG. 2 is a front-elevational view of the instrument test vehicle ofFIG. 1, with parts broken away, to show the relatively rotating partsthereof.

FIG. 3 is an enlarged left side-elevational view of the major part ofthe upper despun platform and showing the frame mounted in isolatedrelationship thereto.

FIG. 4 is a front-elevational view thereof.

FIG. 5 is a schematic illustration of a second embodiment of the testvehicle.

FIG. 6 is similar to FIG. 5, showing a third embodiment.

FIG. 7 is similar to FIG. 5 and showing a fourth embodiment.

FIG. 8 is similar to FIG. 5 and showing a fifth embodiment, which isquite similar to the preferred embodiment of FIGS. 1 through 4.

FIG. 9 shows rectangular reference axes for FIG. 1.

FIG. 10 is an isometric view, with parts broken and parts taken insection of a prior art flexural pivot.

DESCRIPTION FIGS. 5 through 8 illustrate several arrangements of 5 theinstrument vehicle with an isolated frame, in accordance with thisinvention. The simplest form is in FIG. 5, wherein a spinning hollowcylindrical body 10 is illustrated in vertical, axial section. Thespinning body 10 has a certain mass, so that it stabilizes structuressupported thereon against motion due to external forces and tends tomaintain its axis of rotation in one place. The spinning body may be aninert flywheel, or may carry solar cells on the outer surface, while onthe interior thereof, there may be locations for instrumentation,equipment, vessels, or the like. Mounted upon the spinning body 10 is anappropriate mounting location for equipment which can be thus rotatedwithout adverse effect on its operation.

It is known that a despun platform 12 can be rotatably mounted withrespect to this spinning body 10, and relatively rotated at such a speedthat the despun platform has a selected rotation rate with respect toearth-centered space, even zero RPM. This makes the despun platform asuitable place for mounting instrumentation and equipment, the directionof which needs to be controlled with respect to earth-centered space.

As pointed out above, the system may be dynamically stable by employingan inert flywheel for the spinning body, or employ a spinning body whichrotates about the axis of maximum moment of inertia. In the special casewhere the,total transverse moment of inertia is greater than the momentof inertia of the spinning body about the spin axis, it is the teachingof Anthony J. Iorillo US. Pat. No. 3,442,468 that a nutation damper iseffective when mounted upon the despun platform to stabilize thespinning body and the despun platform with respect to nutationalmovement. The employment of the nutation damper on the despun platformprevents tumbling of the structure, and thus provides stability to thestructure.

The despun platform 12 is mounted upon bearing 14 to permit the relativerotation of the spinning body 10 and despun platform 12. Of course,bearing inaccuracies and rotor imbalances cause conical andtranslational wobble motion of the axis of despun platform 12 inearth-centered space, even when the spinning body is adequately dampedfor its nutational motion by the nutation damper on despun platform 12.Wobble is caused by the difference between the axis about which thespinning body rotates, and the axis about which the despun platformrotates with respect to the spinning body. This wobble is usuallyconical, but may be purely translational in a special case, or acombination of both in the general case. The frequency of the wobble isthe same as the spin frequency. In accordance with this invention, pivot16 is mounted on despun platform 12 and carries frame 18 thereon. Pivot16 permits rotation of frame 18 with respect to the platform about anaxis such as to permit free rotation of the frame to stabilize itagainst one component of the wobble. Frame 18 rotates with despunplatform 12, and is thus similary despun. Frame 18 carriesinstrumentation or equipment thereon, the pointing accuracy of which isdesired to be better than the pointing accuracy of any equipmentdirectly mounted upon despun platform 12. When a nutation damper isrequired, it is never mounted on the isolated frame, but on the despunplatform.

In one example, antenna 20 is mounted on frame 18, so that its pointingaccuracy is enhanced, if compared to mounting thereof on platform 12.The directional axis of antenna 20 is in the plane of the paper anddirected to the left in FIG. 5, and is along the X-axis in FIG. 9 and,in order to permit this enhanced accuracy, pivot 16 is a pivot havingits axis perpendicular to the paper, on the Y-axis of FIG. 9. Thus,wobble motion of platform 12 in the plane of the paper of FIG. 5 isisolated from frame 18. With a pivot 16 having a single rotational axis,the motion of the despun platform 12 which would cause nodding of theantenna 20 is isolated. Thus, while a single axis of rotational freedomis all that is necessary for improving pointing accuracy, a pivot ofgreater number of degrees of freedom, such as a ball and socket joint,could be employed to free the frame from rotation on other axes, such asthe X-axis. The character of pivot 16 is described in more detail withrespect to a specific embodiment below. Vehicle 22 thus provides a framewhich is oscillation isolated with respect to and mounted on a platformwhich, in turn, is stabilized by a spinning body. The vehicle 22, asdiscussed above, may be an instrumentation and equipment testbed.Appropriate mounting for employment in gravitational environments isdescribed below. On the other hand, it may be operated in free fall environment.

Vehicle 24 in FIG. 6 is similar to vehicle 22 and has a spinning body26, which may carry instrumentation and equipment, and which rotatablycarries a despun platform 30 on bearing 28. When the total inertia ofthe system in a direction normal to the spin axis is greater than themoment of inertia of the spinning body 26 about its spin axis, inaccordance with the Iorillo patent teaching, the despun platform carriesa nutation damper. The despun platform also carries instrumentation orequipment, in this case antenna 32, the direction of which is fairlyaccurately defined in earthcentered space by means of the rotation ofdespun platform 30 with respect to spinning body 26. In the case ofvehicle 24, frame 34 is mounted upon pivot 36 on the platform 30. Thispivot 36 isolates the frame 34 from wobble. This isolation increases theaccuracy of the pointing of equipment 38, in this case an antenna, inearth-centered space. In accordance with this figure, vehicle 24 is thesame as vehicle 22, except that vehicle 24 has a larger despun platformand has equipment mounted thereon. Where the moment of inertia of theframe 34 about its isolation pivot is sufficiently large, theapplication of damping to this relative motion can provide sufficientdamping in the overall system of spinning body, despun platform andframe that a nutation damper tuned at nutation frequency is notnecessary, but the damped frame tuned closer to the wobble frequencythan any other frequency will be sufficient to provide stability to thesystem.

Vehicle 40, in FIG. 7, again has the spinning body 42 which providesstabilization to a despun platform 44. In this case, the despun platformis principally the inner race of bearing 46. Mounted upon despunplatform 44, by means of pivot 48, is frame 50. As described above,pivot 48 provides isolation for frame 50 with respect to despun platform44, in the direction which aids in pointing accuracy of equipmentmounted upon frame 50. In this case, frame 50 extends through the innerrace of bearing 46 and carries antennas 52 and 54 on opposite ends. Itis clear that the antennas are illustrated as devices which have adirectional axis, the enhanced pointing accuracy of which is desirable.The vehicle 40 provides a structure with a minimized mass of despunplatform, and with a maximized frame 50, which is also despun by beingmounted upon pivot 48, which is intentionally nonrotative about theZ-axis.

When the spinning body is rotating about the axis of maximum moment ofinertia, no nutation damper is necessary on the despun platform in orderto obtain stability. In the case of a spinning body which is rotat ingabout an axis other than the maximum moment of inertia, in accordancewith the teaching of the Iorillo patent, it is necessary to place thenutation damper on the despun platform. A nutation damper is moreeffective, when placed away from the center of gravity of the vehicle.Since the despun platforms l2 and 44 of FIGS. 5 and 7 are fairly small,it is difficult to properly place an effective nutation damper thereon.Nutation damping is required in the special case taught by the Iorillopatent, when the total moment of inertia of the system in any directiontransverse to the spin axis is greater than the moment of inertia of thespinning body about its axis. The nutation damper must be mounted uponthe despun platform, rather than the isolated frame. Thus, in order toachieve effective nutation damping, instead of the use ofa nutationdamper under these difficult conditions, nutation damping can beachieved by damping the motion of the frame with respect to the despunplatform. Since this damping is tuned to the wobble frequency, or atleast its resonant frequency is closer to the wobble frequency than tothe nutation frequency, the application of damping to the joint betweenthe frame and the despun platform does not spe cifically make it anutation damper. However, in the case of sufficient moment of inertia ofthe frame about its isolation axis, sufficient damping is available toprovide vehicle stability, (activated by motion between the despunplatform and the frame).

FIG. 8 schematically illustrates vehicle 56, which is the preferredembodiment of the instrument test platform and vehicle of thisinvention, having a frame 108 which is mounted on and isolated from aplatform 76 which is despun with respect to and stabilized by a spinningbody 58. The vehicle 56 will be generally described with respect to FIG.8, and will be described in more detail by reference to FIGS. 1 through4.

The vehicle 56 has a spinning gyroscopic body 58 which rotates about theZ-axis of FIG. 9. The body 58 may have solar cells on the outer surfacethereof. Body 58 carries various equipment and instruments, for examplein housings 60, secured therein. Some of these housings may be fueltanks of such nature that the change in fuel quantity therein changesthe moment of inertia of the entire spinning body 58. Similarly, thesloshing of fuel in these tanks may also change the moment of inertia.Furthermore, other devices on the spinning body may be mo'vably mountedand, as such, change the moment of inertia or center of mass. This makesthe spinning body non-rigid. The spinning body 58 may be spinning aboutthe axis of maximum moment of inertia. In such a case, no nutationdamping is necessary. However, due to changes in mass distribution onthe spinning body, its axis of rotation may shift. Wobble is causedwhenever the axis of rotation of the spinning body is other than theaxis of rotation of the platform with respect to the spinning body. Thisis different motion than the nutation which becomes a problem when thebody is spinning about other than the axis of maximum moment of inertia.In this latter case, a nutation damper is necessary on the despunplatform to provide the necessary stability to the system.

As previously described, means for the damping of nutation is necessarywhenever the damping ratio of the total system inertia about any axisnormal to the axis of spinning with respect to the moment of inertia ofthe spinning body about its spin axis is greater than one. However,instead of using a nutation ,damper which is tuned to the nutationfrequency, when the frame has a fairly large moment of inertia about itsisolation axis with respect to the despun platform, damping of the frameon that isolation pivot, even if tuned to a frequency which is closer tothe wobble frequency than the nutation frequency, can supply sufficientdamping to prevent loss of system stability due to nutation.

In the schematic showing of FIG. 8, despun platform 62 is mounted uponhearing 64 in the spinning body 58. Motor means 66 is engaged betweenthe spinning body and the despun platform 62 in order to relativelyrotate these two parts. The relative rotation is such that despunplatform 62 may be driven with respect to the rotating body at such aspeed that it is earth-oriented or sun-oriented, or oriented in someother chosen reference coordinates. In this particular case, solarpanels 68 are mounted upon despun platform 62, and the despun platform62 is preferably rotated at such a speed with respect to the spinningbody that it is sun-oriented. In FIGS. 1 and 2, the despun platform 62is illustrated below the spinning body. It is mountedupon bearings inbearing housing 70, and the motor means 66 also acts thereon. The solarpanels 68 extend from the despun platform 62.

In order for the vehicle 56 to be employed as an instrument testplatform, whereby it can be used in nonspace or gravitationalenvironments, pedestal 72 extends upward from a floor support andterminates in a hemispherical air bearing 74, half of which is mountedupon the pedestal and half of which is mounted on despun platform 62. Bymeans of this support, the spinning body 58 can be employed to stabilizeboth the lower despun platform 62 and the upper despun platformhereinafter described.

As is schematically shown in FIG. 8, upper despun platform 76 isrotatably mounted on bearings 78 which have an axis of rotationsubstantially about the Z-axis. Upper despun platform 76 is driven withrespect to the spinning body 58 by motor means 80. Vehicle 56conveniently has two despun platforms, as indicated. Despun platform 62is directed in one set of reference coordinates which could besun-centered, if the vehicle is an earth-orbiting vehicle, or could besun-centered when the vehicle is a test vehicle structure on an earthsurface mounting. The upper despun platform 76 can then be despun at adifferent rate for a different purpose. For example, if the vehicle 56is in earth orbit, despun platform 76 can be rotated with respect tobody 58 at such a speed as to diiect its antennas 82 toward the earth.In those cases where an orbiting vehicle is not desired, but, instead, aground-mounted stabilized structure for use as an instrument platform isdesired, such as by employment of a pedestal 72, it can be despun todirect its antennas 82 or other instrumentation toward the stars, andthe like. In these two illustrations, the relative rotation speed of thetwo despun platforms 62 and 76 with respect to each other is about Irevolution per day.

Referring to FIGS. 1 through 4, the bottom of platform 76 is a disc 84which is mounted flush with the top of rotating body 58. The disc iscarried on a shaft 86 which, in turn, is mounted upon suitable bearingsfor rotation of the upper despun platform 76 with respect to spinningbody 58 and the lower despun platform 62. Framework extends upward fromthe platform. This framework is in the form of uprights 88 and braces90. These are mounted together by suitable angle members. The antennas82 are mounted at the top of the uprights 88, and may be directable bymeans of a pivotal mounting on a pivot axis perpendicular to the planeof the paper in FIG. 3.

In the special case of rotation of the rotating body 58 about an axisother than the maximum moment of inertia, nutation damper 92 is mountedon the despun platform. One of the two movable portions of the nutationdamper 92 is directly mounted upon the despun platform. Nutation damper92 comprises a fixed member 94 mounted upon uprights 88. Member 94 is ofmagnetic material and has an opening therein defined by arcs 96 and 98.Movable member 100 is mounted on a pivot axis on bearing 102 normal tothe plane of the drawing in FIG. 3. Bearing 102 is a special type of lowfriction, low hysterisis bearing with proportional resilient springreturn to the center position, wherein movable member 100 is horizontalin FIG. 3. A suitable bearing is the Bendix flexural pivot, manufacturedby the Bendix Corporation, Utica, N.Y., under the mark Free-Flex." Thisstructure is a frictionless bearing suitable for small angulardeflection and is made of flat, crossed springs supporting therelatively rotatable sleeves.

FIG. 10 shows the prior art flexible pivot. There are two outer sleevemeans or tubular members 241 and 242 and two arcuate inner elements 243and 244. The axially aligned outer members 241 and 242 are axiallyspaced and separated at the peripheral opening. The left tubular member241 is bonded to the upper arcuate element 243. The right tubular member242 is likewise bonded to the lower arcuate element 244. The effectiveangle included between the adjacent edges of the arcuate elements 243and 244 is 30 and this angle can have a range of to 45. The adjacentaxially extending edges of elements 243 and 244 provide stop means tolimit safely the flexing of springs and to limit the relative rotationof members 241 and 242. It is to be noted that arcuate elements 243 and244 respectively including mounting-surface sections 246 and 248 andaxially extending reduced-diameter sections 248 and 249 which projectinto left and right tubular members 242 and 241 and are radially spacedtherefrom. Springs 215 and 217 are firmly bonded in slots in the arcuateelements 243 and 244 so that attachment is maintained under adverseflexing conditions and further so that relative axial movement ortilting between the left and right tubular members 241 and 242 isprevented. Crossed springs 215 and 217 at each end provide a rotationalaxis adjacent to the intersections of the springs. The two identicalconstructions provided by tubular member 241 with arcuate element 243and tubular member 242 with arcuate element 244 can be referred to astwo cylindrical means, each having inwardly projecting arcuatestructures which have finger-like means extending axially. For the leftcylindrical means (members 241 and element 243), the arcuate structureconsists of mounting-surface section 246 and reduceddiameter section 248which form the finger-like means extending axially into and radiallyspaced from the right cylindrical means (member 242 and element 244).For the right cylindrical means, the arcuate structure is formed bymounting-surface section 247 and the reduced-diameter section 249 whichforms the fingerlike means extending axially into and radially spacedfrom the left cylindrical means. With this terminology, the facing partsof arcuate structures are connected by springs 215 and 217 wherebyrelative rotation between the two cylindrical means on a common axis canbe effected. The arcuate structures limit this rotation. The finger-likesections 248 and 249 are spaced radially sufficiently so that contact isprevented during relative rotation of members 241 and 242 when thesprings 215 and 217 are flexed. Thus, the movable member is pivotallymounted and spring-centered. Movable member 100 carries C-shapedpermanent magnets 104 and 106 at its outer ends. These magnets embracethe fixed member 94 at the arcs therein. Relative movement between thefixed member and movable member cause the magnets to set up current inthe fixed member to absorb energy and damp the motion.

FIG. 9 illustrates three rectangular axes as referring to theorientation of the vehicle 56. The Z-axis is the axis of rotation of thespinning body 56, and the axis of rotation of the despun platform 76with respect to the spinning body may be slightly divergent from the Z-axis, due to mechanical tolerances in the bearings and other structuresand due to changes in loading in the non-rigid portion of the rotatingbody. Wobble of the despun platform 76 thus occurs around the Z-axis. Tothe extent that this wobble can be resolved into rotation about theX-axis, the wobble does not affect accuracy, because the X-axissubstantially represents the direction to the point at which theantennas 82 and other equipment mounted on the despun platform aredirected. Thus, only that portion of the wobble which is resolved asrotation around the Y-axis affects accuracy. For this reason, the axisof bearing 102 is parallel to the Y-axis and wobble is isolated on thataxis.

Frame 108 is mounted upon upper despun platform 76. Frame 108 comprisesa directable device 110, such as a laser, or other highly directionalcommunications equipment, signal equipment or. test equipment. The framealso includes that additional equipment as a power supply and controlequipment in housing 112 as is necessary to properly operate and/orcontrol the directable device 110. In the case of a laser, the housing112 carries the power supply and control equipment for the laser whichis desirably directly associated with the laser. All of the movableequipment is thus designated as frame 108, and the frame 108 has acenter of gravity substantially on the axis of bearing 114. Thus, theframe is isolated from that portion of wobble experienced by upperdespun platform 76. The bearing 114 is again a low friction, lowhysteresis rotary bearing having an axis of rotation substantiallyparallel to the Y-axis and having a spring-centering force. Thespringcentering force can be inherent in the bearing construction, suchas when the Bendix flexural pivot is employed, or may be supplied in adifferent construction. The spring rate is such that the naturalfrequency of the mass of frame 108 oscillating on the axis of pivotbearing 114 is tuned to the vehicle wobble frequency to provide maximumisolation.

Damping of the frame 108 with respect to the despun platform 76 isunnecessary, as far as the isolation is concerned, but damping can beprovided to more rapidly reduce unwanted motions of frame 108 due totransient excitation of vehicle 92. Furthermore, in the special case ofa spinning body rotating about other than the axis of maximum moment ofinertia and the mass of frame 108 is a large portion of the mass ofplatform 76, damping of the frame 108 with respect to despun platform 76can provide the necessary nutation damper force stability of suchsystems. While the compromise between the frequency of nutation dampingand the natural frequency of frame may reduce damping performance, insuch operational situations, such a combined damping arrangement can bemore satisfactory from an overall viewpoint.

Damping is accomplished, if desired, in the specific embodimentillustrated in FIGS. 1 through 4 by the installation of a magnetic plate116 on the rear of housing 112. This magnetic plate has an arcuatesurface 118. C-shaped permanent magnet 120 is embraced around the plate116 and is mounted upon disc 84. Thus, half of the damper is mountedupon the frame and the other half, on the despun platform. When relativemotion occurs, the magnet sets up current in the plate to absorb energyfrom the motion. Of course, the magnet and plate can be reversed, orother types of damping devices can alternatively be employed.

Such isolation of the frame 108 without damping provides a substantialreduction in the amount of oscillation in the frame, as compared to theoscillation in the despun platform around the Y-axis. In a particularstructure, the detrimental oscillations have been reduced to aboutone-tenth of their former value by mounting the frame in isolated manneron the platform stabilized by the spinning body. It is clear that thisisolated frame can be employed as a stabilized earthmounted device whichserves as a vehicle for the support of instruments. The severalembodiments of FIGS. 5 through 7 illustrate other manners in which theframe may be mounted but, in each case, isolation is accomplished by apivot axis in a direction suitable for the isolation of the frame fromdisturbing wobble.

This invention having been described in its preferred embodiment, andseveral additional embodiments also described, it is clear that thisinvention is susceptible to numerous modifications and embodimentswithin the ability of those skilled in the art.

What is claimed is:

1. An instrument-carrying vehicle comprising:

a gyroscopic mass rotatable on a first axis;

a despun platform rotatably mounted on said gyroscopic mass to rotatewith respect thereto on a second axis and rotatable at a slower speed inselected coordinates than said gyroscopic mass, the difference betweensaid first and second axes causing wobble at the frequency of theirrelative rotation;

a nutation damper mounted upon said platform to rotate on an axissubstantially normal to said first axis and tuned to a frequency closerto the nutation frequency than any other system frequency to dampnutational movements about the axis of said nutation damper;

an isolated frame pivotally mounted upon said despun platform on a thirdaxis which is oriented substantially normal to said second axis ofrotation, spring means interconnected between said frame and saidplatform for urging said frame rotationally about said third axis to acentered angular position with respect to said platform, said springmeans being related to the mass of said frame so that said frame istuned at a frequency closer to the spin frequency of said spinnable bodythan to any other system frequency and a directable instrument mountedon said frame so that wobble of said despun platform is isolated fromsaid frame and said directable instrument by rotation of said isolatedframe and said directable instrument mounted thereon on said third axis.

2. The instrument-carrying vehicle of claim 1 further including dampingmeans interconnected between said frame and said platform for absorbingenergy from said system as said isolated frame wobbles with respect tosaid platform due to relative rotation of said gyroscopic mass and saiddespun platform.

1. An instrument-carrying vehicle comprising: a gyroscopic massrotatable on a first axis; a despun platform rotatably mounted on saidgyroscopic mass to rotate with respect thereto on a second axis androtatable at a slower speed in selected coordinates than said gyroscopicmass, the difference between said first and second axes causing wobbleat the frequency of their relative rotation; a nutation damper mountedupon said platform to rotate on an axis substantially normal to saidfirst axis and tuned to a frequency closer to the nutation frequencythan any other system frequency to damp nutational movements about theaxis of said nutation damper; an isolated frame pivotally mounted uponsaid despun platform on a third axis which is oriented substantiallynormal to said second axis of rotation, spring means interconnectedbetween said frame and said platform for urging said frame rotationallyabout said third axis to a centered angular position with respect tosaid platform, said spring means being related to the mass of said frameso that said frame is tuned at a frequency closer to the spin frequencyof said spinnable body than to any other system frequency and adirectable instrument mounted on said frame so that wobble of saiddespun platform is isolated from said frame and said directableinstrument by rotation of said isolated frame and said directableinstrument mounted thereon on said third axis.
 2. Theinstrument-carrying vehicle of claim 1 further including damping meansinterconnected between said frame and said platform for absorbing energyfrom said system as said isolated frame wobbles with respect to saidplatform due to relative rotation of said gyroscopic mass and saiddespun platform.